1. Field of the Invention
The present invention relates to a projection screen of television receiver and more particularly, to a rear projection screen having a wide-ranged extinguishing rate which is made to maintain high contrast by widening the area of portions extinguishing the light illuminated on the rear side of screen.
2. Description of the Prior Art
In general, various types of rear projection screens having a wide-ranged extinguishing rate are well known in the art. One such rear projection screen is illustrated in FIGS. 1 and 2.
FIG. 1 is a cross-sectional view of a conventional rear projection screen with a sectionally enlarged view thereof. As shown in the drawing, a Fresnel's lens 1 is formed on the lens side, and lenticules 2 are formed at the television viewer's side. The Fresnel's lens 1 is in the form of concentric circles when viewed from the lens side, and is formed with Fresnel's lens facets 3 having saw teeth cross section. The lenticules 2 are a vertical lines repeated in a horizontal direction when viewed from the viewer's side. The cross section is formed with lenticular facets 4 made of a particular geometrical structure. Diffusers 13 are particles distributed in random within the screen, the refractive index of which particles is different from that of the substrate. On the other hand, extinguishing portions 5 covered a blackener coating layer are formed between each lenticular facet 4.
According to such conventional rear projection screen as shown in FIG. 2, lights of the entire field of Braun tube 6 are emitted through a projection lens 7 and the emitted lights are converted to parallel lights of homogeneous diffusion characteristics through the Fresnel's lens of a screen 8. Then, these lights are diffused vertically and horizontally through the diffusers 13 and horizontally through the lenticule 2.
These diffused lights are sensed by the eyes 9 of the viewer.
The exterior illumination light (noise light) which is an obstructing factor of the contrast being incident from the viewer's side is extinguished by extinguishing portions 5. The contrast depends on where the areas of the lenticular facets 4 and the extinguishing portions 5 are respectively a and b, the ratio of a:b.
In the conventional rear projection screen, since the area b of the extinction portions 5 is relatively smaller than the area of the lenticular facets 4, there has been a defect that the contrast becomes lower under the exterior illumination light.